Solid fuel and oxidizer for underwater propulsion system



Sept. 8, 1970 y L. GREINER 3,527,050

SOLID FUEL AND OXIDIZER FOR UNDERWATER PROPULSION SYSTEM Filed July 18, 1966 01 59. wk: 2 22 hzwomwm 09 pm on om om on 0% v mhw m. Q22 Qoj m0 woz 2m0mmwm INVENTOR, LEONARD GREINER ATTORNEY United States Patent Ofice Patented Sept. 8, 1970 US. Cl. 60-39.0S 9 Claims ABSTRACT OF THE DISCLOSURE An underwater propulsion system employing as a fuel component a flowable slurry of fuel material dispersed in molten sulphur and as the oxidizer component a molten oxidizing agent having a melting point approximating that of sulphur such as a mixture of lithium chlorate and lithium perchlorate.

BACKGROUND OF THE INVENTION This invention realtes to propulsion systems and more particularly to an underwater propulsion system employing as the fuel component a flowable slurry of a solid, readily oxidized material dispersed within molten sulphur.

The copending patent application of Leonard Greiner entitled Method and Compositions for Producing Condensable Combustion Products, Ser. No. 565,697, filed July 18, 1966 now Pat. No. 3,404,531, patented Oct 8, 1968, describes the use of sulphur or sulphur-containing compounds in an underwater propulsion system to produce condensable exhaust gases across a wide spectrum of F ratios.

According to this invention, novel fuel systems consisting of a metal, metal hydride, carbide, or boride dispersed within a sulphur binder have been discovered that can be melted to form a flowable mass and a novel system for combusting such compositions with an oxidizer is provided.

The systems of this invention overcome the problems hitherto associated with prior art underwater propellant systems which employ metals, metal hydrides, borides, and carbides as the primary fuel. The usual methods of utilizing such fuels involves either melting the metal, forming slurries of finely divided fuel material in various organic compounds, or fabricating a fuel grain having a high solids loading of the fuel material for use in a hybrid system. The obvious disadvantages of these systems are respectively, the high temperatures and corrosiveness associated with liquid metals, the degradation of performance associated with the use of organic dispersants selected primarily for physical properties and the difliculty of maintaining proper O/F ratios associated with hybrid propellant systems.

It is an object of this invention to provide a flowable composition of a fuel material and sulphur.

It is another object of this invention to provide an underwater propulsion system for combusting a flowable fuel-sulphur composition.

It is another object of this invention to provide a method for generating a working fluid by combusting a flowable sulphur composition.

It is another object of this invention to provide a fluid bipropellant propulsion system wherein the fuel and oxi dizer are stored in the solid state.

These and other objects of this invention will be readily apparent from the following description with reference to the accompanying drawing wherein:

FIG. 1 is a graph of theoretical performance of a propellant system according to this invention and FIG. 2 is a schematic representation partly in section of an underwater propulsion system according to this invention.

It has been found that compositions comprising a solid fuel material dispersed within a matrix of sul hur form a flowable fluid suitable for use as the fuel component of a bipropellant motor system when heated to above C., the melting point of sulphur. The preferable temperature range is between 120 C. and 135 0., because the viscosity of molten sulphur increases substantially at 135 C., making the slurry more viscous and diflicult to flow. However, above 135 C., the viscosity of sulphur gradually decreases with temperature and operation at such higher temperatures is also possible. The fuel materials usable according to this invention include readily oxidizable metals having melting points above that of sulphur and which are compatible with sulphur such as magnesium, aluminum, zirconium, boron, and titaium, for example. Metal hydrides and borides can also be employed as the fuels if desired. Magnesium is particularly useful in this invention, not only for its thermodynamic properties, but also because its specific gravity of 1.74 closely approximates the specific gravity of molten sulphur of 1.8, thereby reducing any tendency for the fuel material to settle when the sulphur is melted.

Any of the oxidizers mentioned in the above-noted patent application can be used to oxidize the fuel-sulphur slurries of this invention.

Gaseous oxidizers such as oxygen or halogens can be utilized, as can liquid oxidizers such as hydrogen peroxide and interhalogen compounds. However, a preferred embodiment utilizes an oxidizer which is stored in the solid state and is heated to its melting point immediately prior to injection into the combustion chamber. Lithium chlorate and mixtures of lithium chlorate and lithium perchlorate having melting points ranging from about 81 C. to C. are particularly useful in that the melting points are close to the melting point of sulphur. A mixture of lithium chlorate and lithium perchlorate containing 40% lithium perchlorate is particularly useful in that its melting point is 120 C.

FIG. 1 illustrates the theoretical performance of a sulphur-magnesium fuel system when oxidized with lithium chlorate. As can be seen, the performance increases with increased fuel content, however, above about 80% by volume of the fuel component, the viscosity of the slurry is excessive and proper flow of the slurry to the combustion chamber is impaired. Also, it is desirable to have at least approximately 10-15% sulphur in the system to provide for the production of condensable gases at varying O/F ratios.

Referring now to FIG. 2, a torpedo is shown employing a power plant according to this invention. The propeller 2 is driven by a shaft 3 connected to a gear train 4 powered by a turbine 5 which is supplied with working fluid from combustion chamber 6 as is well known in the art. Fuel 7 and oxidizer 8 are stored in a cylindrical tank 9 which is divided into a central fuel portion and an annular oxidizer portion by axially extending cylindrical partition 10. The fuel 7 is a cast solid grain comprising particles of fuel material of the type above described dispersed within a matrix of sulphur particles and is slidably mounted inside partition 10. The oxidizer 8 is in the form of a hollow tube cast from for example a 60/40 mixture of lithium chlorate and lithium perchlorate having a melting point of 120 C. and is slidably mounted on the annulus formed between tank 9 and partition 10. If desired, a liquid or gaseous oxidizer could be employed and if such materials are used, the heat exchanger 11 whose function is explained more fully below would only be required to heat the fuel 7. The ends of the fuel and oxidizer compartments are sealed by sliding pistons 35 and 12 and tank is closed by forward Wall 13 defining a space 25 between the pistons and wall 13 for the pressurizing medium. Combustion chamber 6 is supplied with fuel and oxidizer by supply lines 14 and 15 respectively. A gas take off line 1 connects the combustion chamber to a heat exchanger surrounding the ends of the fuel and oxidizer grains adjacent to the feed lines 14 and 15 whereby the fuel and oxidizer materials may be heated to the fluid state immediately prior to injection into the combustion chamber. Hot gases are fed through line 1 to a heat exchanger coil surrounding the fuel grain (not shown) and then through line 36 to heat exchange coils 11 surrounding the oxidizer. Heat exchanger coil 11 is connected through pipe 16 to the condensuctor 17 which also receives the turbine exhaust gases through line 18. A water pump 20 is driven by a power take off from gear train 4 and supplies sea water from line 31 to the combustion chamber 6 through line to reduce the combustion temperature to tolerable limits and to increase the volume of the working fluid by the formation of high temperature steam. Another line 21 supplies water to the space 25 for pressurizing the fuel and oxidizer pistons and 12.

In operation, an initiator which, for example, may be a small charge of a solid propellant is ignited within the combustion chamber 6 to generate an initial volume of hot gases. These gases flow through heat exchanger to heat the fuel and oxidizer to between 120 C. and 135 C. whereby the materials are rendered flowable. The gases also actuate turbine 5 which in turn drives pump 20 and propeller 2. The pump 20 supplies pressurized water to the space 25 and pressure applied on the forward ends of the fuel and oxidizer grains by piston 35 and 12 causes the fuel and oxidizer which are in the fluid state at the opposite end to be injected into the combustion chamber whereupon operation of the system with the fuel and oxidizer occurs. Pump 20 continually injects water into the combustion chamber 6 to maintain a working fluid temperature of about 1800 C. The exhaust working fluid from the turbine 5 and heat exchanger 11 passes through lines 18 and 16 respectively to the condensuctor 17 where they are admixed with ambient water from line 33 and dumped overboard through line 32.

A suitable fuel grain for use in the above described system comprising 65% magnesium and 35% sulphur by weight was prepared from trimodal magnesium having the following particle size distribution:

Size, mesh: Percent 10 +40 +125 30 +325 20 The magnesium particles are added to the molten sulphur with agitation to assure uniform distribution. The slurry is cast into a suitable mold and allowed to harden.

The above example is merely illustrative of the type of fuel grains employed according to this invention, it being understood that other materials than magnesium can be dispersed within the sulphur. Higher solids loadings of the fuel material in the sulphur are also contemplated provided the viscosity of the melt can be maintained low enough to permit flow of the slurry. Such higher solid loadings can be obtained by modification of the particle size distribution and by the use of surface active agents which function to reduce the tendency of the particles to agglomerate. Although the power plant system described employed a turbine as the prime mover, it is readily apparent that the system can utilize reaction or reciprocating prime movers. Further, while it is preferred to store the fuel and oxidizer in the solid form, the fuel and oxidizer can be stored in fluid form.

I claim:

1. A power plant comprising:

(a) a combustion chamber,

(b) a source of an oxidizer,

(c) means for flowing said oxidizer to said combustion chamber,

(d) a solid grain of particulate fuel material dispersed within a matrix of sulphur,

(e) a container slidably receiving said grain, said container having first and second ends,

(f) means for heating that portion of said grain which is in proximity to said first end to the melting point of sulphur whereby a slurry of fuel material in sulphur is formed at said first end,

(g) fluid communicating means connecting said first end to said combustion chamber, and

(b) means for moving said grain from said second end toward said first end as said slurry is flowed to said combustion chamber.

2. The power plant of claim 1 wherein said source of oxidizer comprises:

(a) a solid grain of oxidizer (b) a container slidably receiving said grain and having a first end adjacent to and communicating with said means for flowing said oxidizer to said combustion chamber and a second end at a distance therefrom (0) means for heating that portion of said grain which is in proximity to said first end to at least the melting point of said oxidizer whereby said oxidizer may be melted and (d) means for moving said grain towards said first end of said container as said melted oxidizer is removed therefrom.

3. The power plant of claim 2 wherein said means for heating said solid grain of fuel material and sulphur and said means for heating said oxidizer grain comprises means for flowing at least a portion of said hot combustion product in heat exchange relationship to said grains.

4. The power plant of claim 3 wherein said oxidizer is selected from the group consisting of lithium chlorate and mixtures of lithium chlorate and lithium perchlorate.

5. The power plant of claim 4 further comprising means for admixing water with said combustion products upstream of said prime mover.

6. A method for generating hot combustion products in an underwater power plant by reaction of a dispersion of a fuel material in sulphur and an oxidizer which comprises:

(a) storing said dispersion and said oxidized separately in solid form,

(b) continuously melting a portion of the sulphur in said dispersion to form a slurry of fuel material in sulphur,

(c) continuously melting a portion of said oxidizer,

(d) continuously feeding said slurry and said melted oxidizer to a combustion chamber, and

(e) reacting said slurry and said oxidizer in said combustion chamber to produce said hot combustion products.

3,527,050 5 6 7. The method of claim 6 wherein said oxidizer is a References Cited material having a melting point from 80 C. to 135 C. UNITED STATES PATENTS and said dispersion and oxidizer are melted by heat exchange from a common heat source. 1,506,323 8/1924 60439-47 8. The method of claim 7 wherein said oxidizer is se- 2,744,380 5/1956 McMlnam et 60-207 lected from the group consisting of lithium chlorate and 5 2,996,877 8/1961 McMlnan et L216 mixtures of lithium perchlorate and lithium chlorate.

9. The method of claim 7 further comprising the step SAMUEL FEINBERG Primary Exammer of admixing water with said hot combustion products U S C1 X R whereby steam is formed and the temperature of said com- 10 bustion products is reduced. 6039.06, 39.47, 39.48, 39.55 

